If your remarks are extemporaneous, you have not prepared them in advance.

如发言是即席，说明没有事先准备好。

At the Academy's annual Summit, Jobs gave a couple of short, extemporaneous talks to a roomful of promising young high school students.

在学年度峰会上，乔布斯对一屋子前途无量年轻高中几次简短即席演讲。